Chunks are loaded with mobs in them although the gamerule says otherwise..
How to reproduce:
- Click "create new world"
- Click "gamerules"
- Click "true" besides "allow mob spawning"
- Create the world
- Execute /kill @e[type=!minecraft:player] until it says "no entities found" (should say it on the first execute, doesn't due to the bug)
- Move and load new chunks
- Execute the command again: new mobs generated
- Type /gamerule doMobSpawning: it says it is set to false.